A mask (reticle) is an important component in an exposure equipment, which needs to be held and supported by a certain means in operation. As illustrated in FIG. 1, a mask 9 is mounted on a mask frame 8 of an exposure equipment, and the mask frame 8 is in a square frame structure; the mask 9 is located at a central position of the mask frame 8, and the stability of the mask 9 is ensured by an adsorption or support structure at the upper and lower edge regions of the mask 9. Specifically, the mask frame 8 is provided thereon with a negative-pressure unit for adsorbing the upper edge region of the mask 9; at the lower edge region of the mask 9, a support portion is provided for supporting the mask 9; when the negative-pressure unit is interrupted, the support portion supports the mask 9, to ensure the reliable security of the mask 9; the support portion is connected with a cylinder piston, and the cylinder piston extends and retracts so as to drive the support portion to move.
Further, the mask frame 8 is supported by a plurality of gas cells (gas packages), such as a first gas cell 6 and a second gas cell 7 indicated in FIG. 1. When the mask 9 is in a normal state, a compressed-dry-air (CDA) supply unit communicating with the gas cells supplies gas to the gas cells; the gas cells support beneath the mask frame 8, thus maintaining the security state of the mask 9. The gas cells are divided into four groups, and provided beneath the four rims of the mask frame 8 respectively; a branch gas-supply pipeline between the CDA supply unit and each group of the gas cells is provided thereon with a pressure-reducing valve and a pressure gauge, such as a first pressure-reducing valve 4 or a first pressure gauge 5 illustrated in FIG. 1; a master gas-supply pipeline at its end proximate to the CDA supply unit is provided thereon with a vent valve 1, a master pressure-reducing valve 2 and a master pressure gauge 3, so that the pressure-reducing valve and the pressure gauge ensures the security of gas supply and ensures that the pressure of the supplied compressed gas can meet the needs. The CDA supply unit, in addition to supplying gas to the gas cells, also provides power source to the above-mentioned cylinder. However, the above structure has drawbacks as follows: once abnormal supply of the CDA supply unit or the negative-pressure unit occurs, it will cause deflation of the gas cells, retraction of the cylinder piston, or lose of the adsorbing force of the negative-pressure unit, resulting in detachment of the mask frame as well as detachment and damages of the mask, which is a very severe loss.